FJ 40 overheating, quickly!

[AJSFJ40]

I have a 1978 FJ40 that heats up very quickly. I can start it and begin to drive it and the tempature gauge goes steadily higher as I drive. Withing a two or three mile span it heats up. I have changed the thermostat and even checked the new one by boiling it on the stove and it opens. Of course the coolant level is full. Coolant is not leaking. Do I have a series internal problem? What are some other things that I can try. I know that the gauge is not faulty as the water is actually to the boiling point. I know someone has an answer. Thanks, AJS

 

[FF LC FREAK]

Have you burped the system? You might have an air bubble in there that is blocking the flow. In case you haven't done this, and don't know the procedure, do this: when the motor is cool, raise the front end with blocks or simply put it on a curb. You want the radiator cap to be the highest point in the system. Take off the radiator cap and start up the engine. Let it run for several minutes so that the coolant starts flowing. If there is an air bubble, this will move it out (i.e. look for bubbles coming up). Replace the radiator cap and go for a drive. Hopefully, this will be all that you need to do.

Good luck!

 

[mooker82]

Stock 2F or engine swap? If its a 2F have you checked than fan clutch? Is your water pump good?

 

[JohnnyC]

have you checked than fan clutch? Is your water pump good?

x2 !!!

 

[WES1977]

i wouldn't think the fan clutch would be bad if it gets hot on the hwy. Stop and go maybe.

 

[FJ40-GARAGE]

First and foremost did you check the gauge?

Check the temperature with a usual thermometer!!

Even had issues with my rig, in the end it was just the old oem gauge showing wrong temperatures.

 

[JohnnyC]

does it heat up quickly and then stay hot/over heat...does it taper off when you slow down?

does it over heat when idleing for a period of time

 

[bajaphile]

My gage reads "H" only at 180F... so check for sure!

 

[MarcoPolo]

Check the temperature with a usual thermometer!!

Nice trick

 

[Coolerman]

Is a 'usual' thermometer an up the tail pipe thermometer?


Juat make sure to clean it off first....

 

[FJ40-GARAGE]

Is a 'usual' thermometer an up the tail pipe thermometer?


Just make sure to clean it off first....

I guess you mean a penetration thermometer for meat ......

If he doesnt stick it thrue his hose it might work.......just dip it in after you took the lid off.

The best thing would be a Thermocap. I need one of these some day

 

[e rock]

Mine did the exact same thing when my coolant (mostly water, really) froze in the lower hose one winter. It took just about exactly 3 miles to boil and start a steam show.

To that end, I would say you probably have a blockage somewhere, or maybe even a collapsing lower hose (it's got the internal spring in it right?). It's possible that the water pump impeller is toast, but I've never heard of that happening without some evidence on the outside - does your fan have any wobble if you grab it and wiggle it back and forth?

 

[Icantdive55]

Start the motor and let it idle for a few minutes. When you feel warmth on the top tank shut it off and IMMEDIATELY place your hand on the cooling fins in several locations. A difference in temp suggests a radiator that needs rodded out. I fought the same issue and tried everything and this is what it turned out to be. Even if you recently had it rodded out check it again. I had taken mine in and it was MISTAKENLY moved from the "to do pile" to the "done pile". Then I spent months figuring it out.

Rod

 

[AJSFJ40]

Now I have a rather stupid question. How can I tell if my fan clutch and water pump are good or bad. Of course the fan turns when running but how can I tell if the water pump is working?

 

[JC39232]

Now I have a rather stupid question. How can I tell if my fan clutch and water pump are good or bad. Of course the fan turns when running but how can I tell if the water pump is working?

Most water pumps have a hold on the bottom side and when it starts going bad, it starts leaking there and you leave coolant/antifreeze/water all over the place (garage, work, Walmart, etc.). There also tends to be a nice sweet smell eminating from the vehicle once it gets hot.

For the fan clutch it can be a little more tricky. You need to grab the fan blades (with engine off) and test it. It should turn, but not easily. If it turns freely it is toast..... Can be hard to determine if it is heading south and not quite completely out though. My 0.02

 

[JC39232]

First and foremost did you check the gauge?

Check the temperature with a usual thermometer!!

Even had issues with my rig, in the end it was just the old oem gauge showing wrong temperatures.

Very stupid question, but is that just a meat or candy thermometer touching the outside of the water neck?

 

[FJ40-GARAGE]

Very stupid question, but is that just a meat or candy thermometer touching the outside of the water neck?

Plumbers around here use them to check the temperature of house heating systems, its just a simple thermometer that gets fixed to the warm water pipes with a spring. I did put it straight on the thermostat housing.

In germany its called *Anlegethermometer* dont know the specific english name for it.

 

[Hugh Heifer]

How about a thermostat going bad? If it does not open and close a tthe appropriate time, the engine will show hot and then, if and when the thermos stat opens it will cool off. If the thermostat closes again (shouldn't) the engine will start showing hot again. Parts are about $25 until you shear of a stud and crack the housing

(I did not do either of these but all things being 40 consider the worst!)

 

[Copenhagen1]

The way I check a fan clutch is to spin it by hand when it is cold. It should have a little tension.

Then crank your truck and let it come up to temperature. Once it is at 180-210*F then you check it two ways. Shut the motor off and spin it by hand again. This time it should be engaged enough that it is a lot harder to turn by hand. If it does not pass this test, in other words, if it still spins easily, you can move to the next test.

While it is still at operating temperature, grab a blade with a gloved hand and have someone start the engine. If the engine doesn't pull the fan out of your hand, you have a bad fan clutch. If you are a little timid about grabbing it with your hand, you can also figure out the direction of spin and hold against it with a wooden or rubber hammer handle. Get in position while the motor is at operating temperature but while it is not running. Again put the hammer handle on a fan blade and try to hold it back while someone starts the engine. If it rips it out of your grasp, your fan clutch is fine. If you can hold it, your fan clutch is toast.

Copenhagen1

 

[bsevans]

Very stupid question, but is that just a meat or candy thermometer touching the outside of the water neck?

You can find this type of thermometer at McMaster-Carr on page 539.